The object of this project is to define and isolate genes coding P. falciparum antigens which are the targets of antibodies which block infectivity of gametocytes of this parasite to mosquitoes. The repetoire of monoclonal antibodies specific to sexual stages of P. falciparum has been expanded to further define target antigens which are shown to include the 230 kDa gamete surface protein of P. faciparum. Cloning genes coding for such antigens has been beset with problems including the immunoselection of DNA clones coding a 70 kDa heat shock protein which appears to be structurally related to the 230 kDa gamete surface protein which was the object of the search. Field studies have shown that human populations exposed to P. falciparum transmission in Papua New Guinea, elaborate antibodies against the 230 kDa and the 48 kDa and 45 kDa gamete surface proteins. Studies with P. vivax in Sri Lanka have shown that certain antigamete antibodies which supress infectivity of the parasite to mosquitoes at high concentrations, enhance infectivity at low concentrations. Human T-cell clones with specificity for P. falciparum gamete antigens have been isolated from the blood of non-immune individuals. These clones have "helper" T-cell phenotypes and their reactivity is histocompatibility antigen restricted. It is planned to use such clones to define the T-cell epitopes of gamete antigens. Analysis of the cross hybridization experiment between clones of P. falciparum is being continued in several laboratories. Cross hybridization has been shown to lead to changes in chromosome size.